Electrical safety device

ABSTRACT

An electrical safety device is disclosed which utilizes a sensor conductor configured in a continuous loop and disposed in an electrical component so as to sense overtemperature or mechanical damage over a length or wide area of the component. The sensor may be simple insulated or non insulated copper wire. A low voltage potential is maintained across the sensor conductor. The sensor circuitry includes ambient temperature compensation.

BACKGROUND

The present invention relates generally to an electrical safety deviceand more specifically to a temperature control device utilizing asensing conductor to provide overtemperature and mechanical damageprotection for extension cords, electrical power cords, and electricalcomponents. The sensing conductor is housed within electrical powercords, cables and components so as to sense temperature changes ormechanical damage over a length of the electrical cable or over thesurface of the electrical component case or internal parts.

Electric powered devices are subject to numerous conditions which canresult in fire, injury by burning, injury by shock or release of toxicfumes. For example, aging or mechanically damaged electrical insulationresults in local shorts and overheating due to large currents. Anotherfrequent cause of overheating in electric motors is mechanical overloador stalling resulting in excessive current. Electrical or electronicdevices which are fan or conduction cooled will overheat if the coolingmedium or transport method fails. A safe, reliable and inexpensivesafety device is needed to sense dangerous electrical conditions such asoverheating and mechanical damage which threaten life and property.

Numerous devices for sensing overtemperature conditions have beenpreviously disclosed and claimed. Up to now, these safety devices havenot enjoyed widespread use due to cost, complexity, electrical ormechanical limitations as well as safety concerns for the device itself.

Some previously disclosed safety devices depend on overcurrentprotection to sense overheating or fire. This type of protection may notbe effective for all parts of a device, especially if the problem ismechanical damage, such as the breaking of some of the strands of acurrent carrying wire or a defective electrical connection due tocorrosion or poor contact. A section of the device or cord may becomedangerously overheated without tripping the overcurrent protectiondevice.

Other safety devices sense the temperature at points along the electriccord or at points within the electrical component. For example, fusiblelinks which melt and open a circuit upon overtemperature conditions havebeen used. Other devices employ thermistors, RTDs or other temperaturesensitive elements which, in conjunction with a sensing and controlcircuit, monitor temperature of the sensor and reduce or cut power tothe device if the sensor overheats. Because these devices detectoverheating conditions only at certain points, the safety devicesprotect only discrete locations; dangerous overheating conditions atother unprotected points may go undetected. In addition, protection of along electrical cord or a number of components is not practical usingthermistors, RTDs, or junction devices due to weight, bulk, and cost.

Linear sensing means provides protection over a continuous length,thereby sensing safety problems over the length of the electrical cord.Linear sensing means can potentially reduce weight, bulk and cost inmany applications. However, linear sensing has several drawbacks. Ifelectrical impedance change in a conductor as a function of temperatureis used as the sensing method, a large temperature change in a shortlength of the conductor is equivalent in impedance change to a smalltemperature difference for the entire length. This leads to difficultiesif the sensing circuitry is made sensitive enough to respond to alocalized high temperature condition; a small ambient temperature changewill cause unwanted alarm, or trip of the unit.

Safety devices which detect temperature over a distance have been usedin applications such as electric heating blankets or in high voltagetransmission lines. Some linear detection devices utilize specializeddielectric coatings between conductors which change electricalcharacteristics as a function of temperature, but these materials add tothe cost, complexity, and, in some cases, reliability problems due toenvironmental, mechanical or aging effects on these materials. Otherlinear detection devices utilize line voltage AC applied to the sensorwire which can present a safety hazard for electric shock. These safetydevices which detect overtemperature over a distance are not designed todetect mechanical damage which could lead to shock or fire dangers.

In U.S. Pat. No. 4,577,094 issued Mar. 18, 1986, a sensory and controldevice for electrical heating apparatus is disclosed and claimed. Thesensory function is performed by a linear conductor with a positivetemperature coefficient, placed so as to sense and control heat producedby a heating element. No method is disclosed for ambient temperaturecompensation. Furthermore, the sensory wire is not disposed to detectmechanical damage to the protected device.

In U.S. Pat. No. 2,501,499 issued Mar. 21, 1950, an electric heatingcontrol device is disclosed which incorporates ambient temperaturecompensation. No method is disclosed for sensing mechanical damage to adevice.

Until now, no device has been available for wide application in electricpower cords, extension cords, and other electrical devices to senseovertemperature or mechanical damage over a wide area of an electricalcomponent and which is reliable, inexpensive, and safe. The neededsafety device should utilize low cost sensing wire and low costmanufacturing processes. It should provide the safety of low voltagesensing. It should compensate for ambient temperature to reduce spurioustrips and improve sensitivity. And it should provide expanded mechanicaldamage sensing protection to further protect the user from electricalshock as well as fire hazards.

SUMMARY

The present invention addresses the need for a safety device forelectrical components which can sense either overtemperature conditionsor possible dangerous mechanical damage to the component over a widearea. It consists of a continuous loop of a low cost sensing conductor,such as simple copper wire, positioned in the electrical component sothat at least part of the conductor loop is positioned between anenergized part of the electrical component and the outside surface ofthe component, a reference conductor placed to sense ambient temperatureand a sensor/controller unit.

Power for the electrical component to be protected is supplied from apower source through the sensor/controller unit. The sensor/controllerunit comprises two circuit functions. The sensor circuit measures thedifference between the resistance of the sensor and reference conductorsby imposing a low voltage potential across the conductors. Thecontroller circuit de-energizes the electrical component when thedifference in resistance of the sensor conductor and the referenceconductor reach a predetermined value, as would be caused by anovertemperature condition of the electrical component as sensed by thesensor conductor.

The position of the sensor conductor also results in a high probabilityof sensor conductor breakage if the electrical component is damaged. Thesensor/controller senses this breakage as loss of continuity (highresistance) of the sensor conductor and interrupts power to theelectrical component. This additional personal/property protection isprovided to reduce the possibility of exposure to energized parts.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood with regard to the followingdescription, appended claims, and accompanying drawings where:

FIG. 1 is a block diagram of the electrical safety device;

FIG. 2 is a schematic diagram of the preferred embodiment of the presentinvention;

FIG. 3 is a schematic diagram of an alternative embodiment of thepresent invention;

FIG. 4 is a perspective drawing showing a method of placement of thesensing conductor in a power cord;

FIG. 5 is a cross-section of FIG. 4;

FIG. 6 is a perspective drawing showing another method of placement ofsensor conductor in a power cord;

FIG. 7 is a cross-section of FIG. 6;

FIG. 8 is a perspective drawing showing yet another placement of sensorconductor in an electrical cord;

FIG. 9 is a cross-section of FIG. 8;

FIG. 10 is a perspective drawing showing still another placement ofsensor conductor in an electrical cord;

FIG. 11 is a cross-section of FIG. 10;

FIG. 12 is a perspective drawing showing yet another placement of sensorconductor in an electrical cord;

FIG. 13 is a cross-section of FIG. 12;

FIG. 14 is a perspective drawing showing the preferred embodiment of theinvention adapted to an electrical extension cord;

FIG. 15 is a detail cutaway of FIG. 14 showing the location of sensorconductors disposed in the insulated portion of cord;

FIG. 16 is a cutaway detail of the extension cord receptacle of FIG. 14;

FIG. 17 is a perspective drawing showing the present invention utilizedin an appliance;

FIG. 8 is a cross section of the appliance cord of FIG. 17;

FIG. 9 is a perspective drawing showing the present invention utilizedin an electronic component;

FIG. 20 is a cross-section of the case wall of FIG. 19;

FIG. 21 is a perspective drawing showing the use of the presentinvention in an ornamental light string.

DETAILED DESCRIPTION

FIG. 1 is a block diagram of the present invention. An electrical powersource 1 supplies line voltage 2 to sensor/controller 3.Sensor/controller 3 in turn supplies power to a current carrying means 4in protected electrical component 5. Sensor conductor 7 is positionedbetween the current carrying means 4 and an outside surface ofelectrical component 5, and forms a continuous loop connected tosensor/controller 3. Reference conductor 8 is also connected tosensor/controller 3 and is positioned to sense ambient temperature ofthe electrical component. Both sensor conductor 7 and referenceconductor 8 are chosen to have a similar temperature coefficient ofresistance. Sensor/controller 3 comprises a means to measure thedifference in resistance of the sensor and reference conductors byproducing a low voltage potential across the conductors. Low voltage ismeant to be a potential which will not result in a substantial shockhazard (nominally less than 30 volts), but in its preferred embodiment,the potential is less than one volt. When the difference in resistanceof the sensor and reference conductor reaches a set value (representingan overheated condition of the sensor conductor), the sensor/controllerinterrupts power to the current carrying means of the electricalcomponent. In the preferred embodiment, power remains interrupted untilthe overtemperature condition is removed and the sensor/controller isreset by the user. The sensor/controller also includes a means whichdetects continuity of the sensor conductor and interrupts power to thecurrent carrying means 4 of the electrical device 5 upon loss ofcontinuity.

The location of sensor conductor 7 is critical to the operation of theinvention. Placed between an energized wire or part of the protectedelectrical component and the outside surface of the protected device,the sensor conductor performs two separate safety function. First, itsenses an overtemperature condition whether from inside or outside theprotected device, and, secondly, the sensor conductor placement resultsin a high probability that the sensor conductor will be broken as aresult of physical damage such as shock, trauma, cutting, deterioration,or corrosion to the protected component prior to the energized wire orpart being exposed. Since the sensor/controller detects loss ofcontinuity, the protected electrical component will be de-energizedbefore the energized wire or part is exposed. The gauge or thickness ofthe sensor conductor as well as the sensor conductor material andplacement in the protect device are chosen to increase the probabilityof sensor conductor breakage upon one of the aforementioned conditions.Safety is further improved by use of a low voltage applied to the sensorconductor, so that even if exposed or touched, the sensor conductor willnot present a shock hazard.

It is necessary for at least a portion of the sensor conductor to beplaced between the current carrying element or energized wire or part ofthe protected electrical component and an outside surface of theprotected electrical component. In the preferred embodiment asubstantial portion of the sensor conductor is placed in this positionto increase the length of sensor conductor that is in a protectiveposition as described earlier. Ideally, multiple paths and loops ofcontinuous sensor conductor would be distributed in the protectedcomponent as described, so that the maximum amount of the protecteddevice is protected from overheating. Any feasible mishandling or damageto the device would result in breakage of the sensor conductor and theresulting de-energizing of the component. Another benefit of increasedlength or the sensor conductor is that the impedance of the sensorconductor loop is increased, reducing the current requirements of thedevice for a given reference voltage maintained across the bridgecircuit of the embodiment discussed later.

Likewise, the placement of the reference conductor is important to theoperation of the device. Ideally, the reference conductor senses onlyambient temperature and therefore would be located remote from the restof the protected component. Often this is not practical, especially inconsumer electrical equipment, so the reference conductor could belocated on the component or piece of equipment in a position which wouldsense ambient temperature and be in a location away from possible heatproducing parts of the component. This may commonly be on an outsidesurface, such as the back or bottom of the component.

FIG. 2 shows a schematic diagram of the preferred embodiment of thepresent invention. AC line voltage is supplied from AC plug 10 to acurrent carrying means 11 of electrical component 12 through aninterrupting means (control contacts 13 of protective relay 14). Sensorconductor 16 disposed substantially between the current carrying means11 and the surface of the electrical component 12 consists of aconductor, such as copper wire with a positive temperature coefficientof resistivity and forms one leg of a bridge circuit 15. Referenceconductor 17, a conductor with a similar temperature coefficient ofresistivity as the sensor conductor, forms a second leg to bridgecircuit 15. Output of the bridge 15 is connected to an operationalamplifier or comparator 20 whose output energizes or de-energizescontrol relay 14 through relay driver 21. Control relay contacts 31latch control relay 14 in the energized position and control indicatorLEDs for “tripped” 32 and “on” 33. Momentary “on” switch 22 turns onelectrical component 12 and momentary “off” switch 23 trips or turns offthe component 12. Momentary “on” switch 22 also ensures that the devicehas to be manually “reset” to restore current to the electricalcomponent after a trip condition. Variable conductor 19 is used toadjust the trip point of the device by balancing or unbalancing thebridge circuit 15 as required. Power supply 24 comprises a circuitbreaker or fuse 29 for load protection, isolation transformer 25, bridgerectifier 26 and voltage regulators 27 and 28. Voltage regulator 27supplies circuit and control voltage to the operational amplifier,driver, relay and indicator circuits and is typically 5-12 VDC. Voltageregulator 28 supplies a regulated voltage to the bridge circuit and istypically less than one volt.

The location of sensor conductor 16 and reference conductor 17 in bridge15, and the connection of operational amplifier 20 and relay driver 21are chosen so an increasing temperature at sensor conductor 16 resultsin de-energizing control relay 14 and therefore de-energizing thecurrent carrying means of electrical component 12. This arrangementensures “fail safe” operation upon loss of power supply 24, or failure(opening) of sensor conductor 16, operational amplifier 20, relay driver21, or control relay 14. The use of a sensor conductor with a positivetemperature coefficient of resistivity in this arrangement also acts asa continuity sensor in that a break anywhere in the sensor conductorloop will result in a “high” resistance as sensed by the bridge circuitand open control relay 14, thereby de-energizing the protectedcomponent.

A fault in the sensor/controller module 31 could be protected by aportion of the sensor wire embedded in the module 31. However, dependingon its location, the reference conductor 17 may become overheated aswell, thereby preventing a sensor conductor 16 induced thermal trip. Togive additional protection for such a case, a fusible link 30 isincluded in the module to turn off the module 3 and electrical component12 upon module overtemperature.

FIG. 3 is an alternative embodiment of the present invention. A solidstate switch such as a triac 36 is used to interrupt the currentcarrying means 11 of electrical component 12. The triac is controlled bythe output of operational amplifier 20 through an isolated solid statecoupler such as an opto-coupler 35. Low voltage DC for the bridgecircuit 15 and operational amplifier 20 is supplied through a rectifierbridge 34, solid state breakdown device such as a zener diode 38, anddropping resistor 39. This device could be used in a control applicationbecause no manual reset is required to restore current to the electricalcomponent 12.

FIG. 4 shows a method of placement of the sensor conductor 40 in a powercord 41. The sensor conductor 40 is parallel to current carryingconductors 42 and located in the insulation portion 43 between thecurrent carrying conductors 42 and the outside of the insulation. Thesensor conductors 40 are connected at the ends to form a continuous loopat one end (not shown).

FIG. 5 is a cross-section of FIG. 4 showing placement of sensorconductors 40.

FIG. 6 shows another method of placement of sensor conductor 60 in apower cord 61. Sensor conductor 60 is fashioned in a “sinusoidal” or“snake” pattern in the insulation portion 62 of the power cord 61between the current carrying conductors 63 and the outside of the powercord 61. The particular shape of the sensor conductor placementincreases the flexibility of the power cord and reduces the possibilityof inadvertent damage to the sensor conductor due to normal handling anduse of the cord.

FIG. 7 is a cross-section of FIG. 6 showing placement of sensorconductor 60.

FIG. 8 shows yet another placement of sensor conductor 80 in anelectrical cord 81. Sensor conductor 80 is wound in a helical shape andplaced parallel to current carrying conductors 82 in the insulatedportion 83 of the cord 81 between the current carrying conductor 82 andthe outside of the cord 81. The particular shape of the sensor conductorplacement increases the flexibility of the power cord and reduces thepossibility of inadvertent damage to the sensor conductor due to normalhandling and use of the cord.

FIG. 9 is a cross-section of FIG. 8 showing placement of sensorconductor 80.

FIG. 10 shows still another placement of sensor conductor 100 in anelectrical cord 101. Sensor conductor is wound in a helical shapesurrounding current carrying conductors 102 in the insulated portion 103of the cord. A second sensor conductor 104 is shown in the center of thecord to allow forming a continuous loop from one end of the cord. Theparticular shape of the sensor conductor placement increases theflexibility of the power cord and reduces the possibility of inadvertentdamage to the sensor conductor due to normal handling and use of thecord.

FIG. 11 is a cross-section of FIG. 10 showing placement of sensorconductors 100 and 104.

FIG. 12 shows yet another placement of sensor conductor 120 in anelectrical cord 121. Sensor conductor 120 consists of a conductiveelastomer which is extruded as separate strips in the insulation portion122 during manufacture. The sensor conductor 120 is parallel to, andlocated between, current carrying conductor 123 and the outside ofelectrical cord 121.

FIG. 13 is a cross-section of FIG. 12 showing location of sensorconductor 120.

FIG. 14 shows the preferred embodiment of the invention adapted to anelectrical extension cord. Plug-in module 140 contains thesensing/controller circuitry (not shown), AC plug ends 141, “on/reset”switch 142, “off” switch 143, “on” LED 144, “off” LED 145, and referenceconductor 146. Electrical cord 147 connects plug-in module 140 withreceptacle end 148.

FIG. 15 is a detail cutaway of FIG. 14 showing the location of sensorconductors 150 disposed in the insulated portion of cord 147 betweencord conductors 151 and the outside of cord 147.

FIG. 16 is a cutaway detail of the extension cord receptacle 148 showingthe sensor wire 160 disposed in the insulated body portion of thereceptacle between the receptacle conductors (not shown) and the outsidesurface of the receptacle. The sensor conductor 160 is connected to forma continuous loop from the plug in module end.

FIG. 17 shows the present invention utilized in an appliance.Sensor/controller module 170 is located inside the appliance. The powercord 171 is connected to the module and an insulated sensor conductor174 is distributed on the inside surface of the appliance structure aswell as on various stationary components such as the motor frame 173within the appliance. Sensor wire 180 in power cord 171 (see FIG. 18) isconnected with sensor conductor 174 in the appliance to form acontinuous loop from the sensor/controller module 170. Power cord sensorconductor 180 is disposed in the insulated portion 182 of the power cordbetween the power conductor 181 and the outside of the power cord 171.The reference conductor (not shown) may be located on an outside surfaceof the appliance such as the bottom or back of the appliance.

FIG. 19 shows the present invention utilized in an electronic component.Sensor/controller module 192 may be located on the chassis 1 91 or onthe plug end (not shown). Sensor conductor 193 is disposed on thechassis in the vicinity of various components. A sensor ribbon 194 isbonded to the inside of the case 195 and forms a continuous loop withsensor conductor 193 when the case is attached to the chassis receptacle196 by means of a case plug 197. FIG. 20 shows a cross-section of thecase wall showing the sensor ribbon 193 bonded to the inside surface ofthe case wall 200.

FIG. 21 shows the use of the present invention in an ornamental lightstring. Plug 210 supplies power to the lights 211 through cord 213 andsensor/controller module 214. Sensor conductors 215 are distributed incord 213 and light sockets 216. Sensor/controller module 214 containscombination on/reset switch and indicator light 217 and combination offswitch and trip light 218. Reference conductor (not shown) is located onthe back of sensor/controller module 214.

Although the description above contains many specifications, theseshould not be construed as limiting the scope of the invention but asmerely providing illustrations of some of the presently preferredembodiments of this invention. For example, a sensor conductor andreference conductor with a negative temperature coefficient ofresistivity could be utilized in the present invention. This wouldrequire a separate continuity sensor for the sensor conductor since anopen in the sensor conductor would be equivalent to a “low” sensedtemperature.

Thus the scope of the invention should be determined by the appendedclaims and their legal equivalents, rather than by the examples given.

1. An electrical cord safety device, the device comprising: an electrical power cord comprising at least one current carrying conductor, insulation surrounding the current carrying conductor, and a cord outside surface; a sensor conductor for sensing temperature in the said electrical power cord, the said sensor conductor disposed in the insulation of the said electrical power cord as a continuous loop, the said sensor conductor having a positive temperature coefficient of resistivity, and further disposed between the said current carrying conductor and the said outside surface and in a manner such that continuity of the said sensor conductor is lost upon mechanical damage to the electrical power cord before the current carrying conductor is exposed, whereby the said sensor conductor further comprises a continuity detecting means; a reference conductor disposed in the vicinity of the said electrical power cord for sensing ambient temperature; and a control circuit connected to the said sensor conductor and the said reference conductor, the said control circuit comparing a first electrical quantity representative of the said sensor conductor temperature and a second electrical quantity representative of the said reference sensor temperature and interrupting current to the said current carrying conductor upon a predetermined difference between the said first electrical quantity and the said second electrical quantity.
 2. The device of claim 1 wherein the said sensor conductor is disposed in a parallel relationship with the said current carrying conductor.
 3. The device of claim 1 wherein the said sensor conductor is disposed in a sinusoidal shape along the said current carrying carrying conductor.
 4. The device of claim 1 wherein the said sensor conductor is disposed in a helical shape surrounding the said current carrying conductor.
 5. The device of claim 1 wherein the said sensor conductor comprises a conductive polymer strip.
 6. An electrical safety device, the device comprising: a case for an electrical component, the said case comprising an outside surface; a current carrying conductor disposed inside the said case; a sensor conductor for sensing temperature in the said case, the said sensor conductor disposed in the said case as a continuous loop, the said sensor conductor having a positive temperature coefficient and further disposed between the said current carrying conductor and the said outside surface of the said case and in a manner such that continuity of the said sensor conductor is lost upon mechanical damage to the said case before the said current carrying conductor is exposed, whereby the said sensor conductor further comprises a continuity sensing means; a reference conductor disposed in the vicinity of the said case for sensing ambient temperature; and a control circuit connected to the said sensor conductor and the said reference conductor, the said control circuit comparing a first electrical quantity representative of the said sensor conductor temperature and a second electrical quantity representative of the said reference sensor temperature and interrupting current to the said current carrying conductor upon a predetermined difference between the said first electrical quantity and the said second electrical quantity whereby the said device acts to detect a high temperature in the said case as compared to the said ambient temperature.
 7. The device of claim 6 wherein the said case comprises an inside surface and the said sensor conductor is a conductive foil disposed in the said inside surface of the said case.
 8. An electrical power cord including an insulated electrical conductor portion for use in connection with a control circuit configured for measuring resistance, said control circuit configured for initiating a control action upon its detection of a predetermined resistance, said electrical power cord being substantially elongate, having a length, and comprising: an electrical power cord portion itself including along its length a substantially elongate current carrying conductor portion configured to pass electrical current, said current carrying conductor portion extending substantially straight along said length of said insulated electrical conductor portion such that said current carrying conductor portion is approximately as long as said insulated electrical conductor portion; insulation at least partially surrounding said current carrying conductor portion, said insulation defining an insulated electrical conductor outside surface portion; and a substantially elongate sensor conductor portion for sensing temperature within said insulation, said elongate sensor conductor portion extending along said length of said insulated electrical conductor portion but curving at least partially laterally relative to said conductor portion length such that said elongate sensor conductor portion is longer than said insulated electrical conductor portion, said sensor conductor portion comprising a material having a change in resistance with temperature whereby a change in the temperature of said sensor conductor portion results in a change in resistance of said sensor conductor portion, and said sensor conductor portion further disposed between said current carrying conductor portion and said insulated electrical conductor outside surface portion in a manner such that continuity of said sensor conductor portion tends to be lost upon mechanical damage of said insulation before said current carrying conductor portion is exposed, such that said sensor conductor portion provides a dual function of indicating mechanical damage as well as the function of indicating heating of said insulation to allow said control circuit to initiate said control action upon a predetermined resistance of said sensor conductor portion.
 9. The electrical power cord as claimed in claim 8, wherein said sensor conductor portion has a positive temperature coefficient of resistivity.
 10. The electrical power cord as claimed in claim 8, wherein said sensor conductor portion is disposed in a helical relationship about the current carrying conductor portion, said helical relationship causing said sensor conductor portion to be longer than said current carrying conductor portion for a given length of insulated electrical conductor portion.
 11. The electrical power cord as claimed in claim 8, wherein said sensor conductor portion is disposed in a sinusoidal relationship about the current carrying conductor portion, said sinusoidal relationship causing said sensor conductor portion to be longer than said current carrying conductor portion for a given length of insulated electrical conductor portion.
 12. The electrical power cord as claimed in claim 8, wherein said sensor conductor portion is one of a plurality of coparallel strips disposed radially about the current carrying conductor portion.
 13. An electrical power cord including an insulated electrical conductor portion for use in connection with a control circuit configured for measuring resistance, said control circuit configured for initiating a control action upon its detection of a predetermined resistance, said electrical power cord being substantially elongate, having a length, and comprising: an electrical power cord portion itself including along its length a substantially elongate current carrying conductor portion configured to pass electrical current, said current carrying conductor portion extending substantially straight along said length of said insulated electrical conductor portion such that said current carrying conductor portion is approximately as long as said insulated electrical conductor portion; insulation at least partially surrounding said current carrying conductor portion, said insulation defining an insulated electrical conductor outside surface portion; and a substantially elongate sensor conductor portion for sensing temperature within said insulation, said elongate sensor conductor portion extending along said length of said insulated electrical conductor portion but curving at least partially laterally relative to said conductor portion length such that said elongate sensor conductor portion is longer than said insulated electrical conductor portion, said sensor conductor portion comprising a material having a change in resistance with temperature whereby a change in the temperature of said sensor conductor portion results in a change in resistance of said sensor conductor portion, and said sensor conductor portion being noninsulated, and said sensor conductor portion being further disposed between said current carrying conductor portion and said insulated electrical conductor outside surface portion in a manner such that continuity of said sensor conductor portion tends to be lost upon mechanical damage of said insulation before said current carrying conductor portion is exposed, such that said sensor conductor portion provides a dual function of indicating mechanical damage as well as the function of indicating heating of said insulation to allow said control circuit to initiate said control action upon a predetermined resistance of said sensor conductor portion.
 14. The electrical power cord as claimed in claim 13, wherein said sensor conductor portion has a positive temperature coefficient of resistivity.
 15. The electrical power cord as claimed in claim 13, wherein said sensor conductor portion is disposed in a helical relationship about the current carrying conductor portion, said helical relationship causing said sensor conductor portion to be longer than said current carrying conductor portion for a given length of insulated electrical conductor portion.
 16. The electrical power cord as claimed in claim 13 wherein said sensor conductor portion is disposed in a sinusoidal relationship about the current carrying conductor portion, said sinusoidal relationship causing said sensor conductor portion to be longer than said current carrying conductor portion for a given length of insulated electrical conductor portion.
 17. The electrical power cord as claimed in claim 13, wherein said sensor conductor portion is one of a plurality of coparallel strips disposed radially about the current carrying conductor portion.
 18. An electrical power cord including an insulated electrical conductor portion for use in connection with a control circuit configured for measuring resistance, said control circuit configured for initiating a control action upon its detection of a predetermined resistance, said electrical power cord being substantially elongate and comprising: an electrical power cord portion itself including along its length a substantially elongate current carrying conductor portion configured to pass electrical current; insulation at least partially surrounding said current carrying conductor portion, said insulation defining an insulated electrical conductor outside surface portion; and a plurality of substantially elongate, noncontacting sensor conductor portions for sensing temperature within said insulation, said sensor conductor portions not contacting each other, at least one of said sensor conductor portions comprising a material having a change in resistance with temperature whereby a change in the temperature of said sensor conductor portion results in a change in resistance of said sensor conductor portion, and said same one of said sensor conductor portions further disposed between said current carrying conductor portion and said insulated electrical conductor outside surface portion in a manner such that continuity of said same one of said sensor conductor portions tends to be lost upon mechanical damage of said insulation before said current carrying conductor portion is exposed, such that said same one of said noncontacting sensor conductor portions provides a dual function of indicating mechanical damage as well as the function of indicating heating of said insulation to allow said control circuit to initiate said control action upon a predetermined resistance of said same one of said sensor conductor portions.
 19. The electrical power cord as claimed in claim 18, wherein said same one of said sensor conductor portions is substantially straight and parallel to said current carrying conductor portion.
 20. The electrical power cord as claimed in claim 18, wherein said same one of said sensor conductor portions is disposed in a helical relationship about the current carrying conductor portion.
 21. The electrical power cord as claimed in claim 18, wherein said same one of said sensor conductor portions is disposed in a sinusoidal relationship about the current carrying conductor portion.
 22. The electrical power cord as claimed in claim 18, wherein said same one of said sensor conductor portions is one of a plurality of coparallel strips disposed radially about the current carrying conductor portion.
 23. An electrical power cord including an insulated electrical conductor portion for use in connection with a control circuit configured for measuring resistance, said control circuit configured for initiating a control action upon its detection of a predetermined resistance, said electrical power cord being substantially elongate and comprising: an electrical power cord portion itself including along its length a substantially elongate current carrying conductor portion configured to pass electrical current; insulation at least partially surrounding said current carrying conductor portion, said insulation defining an insulated electrical conductor outside surface portion; and a plurality of substantially elongate and parallel sensor conductor portions for sensing temperature within said insulation, at least one of said sensor conductor portions comprising a material having a positive temperature coefficient of resistivity, and said same one of said sensor conductor portions further disposed between said current carrying conductor portion and said insulated electrical conductor outside surface portion in a manner such that continuity of said same sensor conductor portion tends to be lost upon mechanical damage of said insulation before said current carrying conductor portion is exposed, such that said same one of said sensor conductor portions provides a dual function of indicating mechanical damage as well as the function of indicating heating of said insulation to allow said control circuit to initiate said control action upon a predetermined resistance of said sensor conductor portion.
 24. The electrical power cord as claimed in claim 23, wherein said plurality of substantially elongate and parallel sensor conductor portions comprises two or more sensor conductor portions.
 25. The electrical power cord as claimed in claim 23, wherein said plurality of substantially elongate and parallel sensor conductor portions comprises three or more sensor conductor portions.
 26. An electrical power cord including an insulated electrical conductor portion for use in connection with a control circuit configured for measuring resistance, said control circuit configured for initiating a control action upon its detection of a predetermined resistance, said electrical power cord being substantially elongate and comprising: an electrical power cord portion itself including along its length a substantially elongate current carrying conductor portion configured to pass electrical current, said current carrying conductor portion extending along said length of said insulated electrical conductor portion such that said current carrying conductor portion is approximately as long as said insulated electrical conductor portion; insulation at least partially surrounding said current carrying conductor portion, said insulation defining an insulated electrical conductor outside surface portion; and a substantially elongate sensor conductor portion for sensing temperature within said insulation, said elongate sensor conductor portion extending along said length of said insulated electrical conductor portion but curving at least partially laterally relative to said conductor portion length and disposed in a helical relationship about the current carrying conductor portion such that said elongate sensor conductor portion is longer than said insulated electrical conductor portion, said sensor conductor portion comprising a material having a change in resistance with temperature whereby a change in the temperature of said sensor conductor portion results in a change in resistance of said sensor conductor portion, and said sensor conductor portion further disposed between said current carrying conductor portion and said insulated electrical conductor outside surface portion in a manner such that continuity of said sensor conductor portion tends to be lost upon mechanical damage of said insulation before said current carrying conductor portion is exposed, such that said sensor conductor portion provides a dual function of indicating mechanical damage as well as the function of indicating heating of said insulation to allow said control circuit to initiate said control action upon a predetermined resistance of said sensor conductor portion.
 27. The electrical power cord for use in connection with a control circuit configured for measuring resistance as claimed in claim 26, wherein said current carrying conductor portion extends substantially straight along said length of said insulated electrical conductor portion.
 28. An electrical power cord including an insulated electrical conductor portion for use in connection with a control circuit configured for measuring resistance, said control circuit configured for initiating a control action upon its detection of a predetermined resistance, said electrical power cord being substantially elongate, having a length, having a transverse cross section having a substantially constant outer periphery, and comprising: an electrical power cord portion itself including along its length a substantially elongate current carrying conductor portion configured to pass electrical current, said current carrying conductor portion extending along said length of said insulated electrical conductor portion and located substantially consistently within said transverse cross section of said electrical conductor portion along the length of said electrical conductor portion; insulation at least partially surrounding said current carrying conductor portion, said insulation defining an insulated electrical conductor outside surface portion; and a substantially elongate sensor conductor portion for sensing temperature within said insulation, said elongate sensor conductor portion extending along said length of said insulated electrical conductor portion and located at different locations within said transverse cross section of said electrical conductor portion along the length of said electrical conductor portion such that said elongate sensor conductor portion is longer than said insulated electrical conductor portion, said sensor conductor portion comprising a material having a change in resistance with temperature whereby a change in the temperature of said sensor conductor portion results in a change in resistance of said sensor conductor portion, and said sensor conductor portion further disposed between said current carrying conductor portion and said insulated electrical conductor outside surface portion in a manner such that continuity of said sensor conductor portion tends to be lost upon mechanical damage of said insulation before said current carrying conductor portion is exposed, such that said sensor conductor portion provides a dual function of indicating mechanical damage as well as the function of indicating heating o said insulation to allow said control circuit to initiate said control action upon a predetermined resistance of said sensor conductor portion.
 29. The electrical power cord for use in connection with a control circuit configured for measuring resistance as claimed in claim 28, wherein said elongate sensor conductor portion is disposed in a helical relationship about the current carrying conductor portion. 